Optical recording medium reproducing apparatus

ABSTRACT

This invention is applicable to an apparatus using an optical pickup to reproduce information recorded on an optical recording medium. By enabling the automatic setting of reproducing conditions applicable to a mounted optical recording medium so that a plurality of types of optical recording media can be compatibly mounted, the present invention enables recorded information to be reliably reproduced even if the recording medium has a low recording density.

This is a divisional of application Ser. No. 08/716,266, filed Sep. 24,1996, now U.S. Pat. No. 6,034,936.

TECHNICAL FIELD

The present invention relates to an optical recording medium reproducingapparatus, and in particular, to an optical recording medium reproducingapparatus adapted to reproduce optically recorded information recordedon an optical recording medium by irradiating the medium with a lightspot of a laser beam.

BACKGROUND ART

Compact discs (CDs) have conventionally been used as optical recordingmedium reproducing apparatus of this kind, wherein the disc as anoptical recording medium is irradiated via an optical system 0.45 innumerical aperture (NA) with a laser beam 780[nm] in wave length whichis generated by a laser diode.

In recent years, however, new laser beam sources with a wave lengthsmaller than 780[nm] (for example, red=680[nm], and semiconductor lasersof green and blue) have been developed as light sources for opticalrecording medium reproducing apparatuses. These new laser beam sourcesserve to implement recording medium reproducing apparatuses that canreproduce recording media with a higher recording density than compactdiscs. These recording medium reproducing apparatuses that can reproducerecording media with a higher recording density than compact discsdesirably have a compatible reproducing function that also enablesconventional compact discs (CDs) to be reproduced.

The diameter of the light spot that can be formed by a laser beam of alarge wave length is selected so as to be somewhat larger than the widthW1 of pits P1 formed in the compact disc as recorded information asshown by reference L1 in FIG. 1(A). This allows the light spot L1 toconstantly lie across the width W1 during movement when entering the pitP1 from land to scan it.

A sum signal (hereafter referred to as an "RF signal") can thus beobtained from an optical pickup based on light reflected from thecompact disc because of the light spot L1 in FIG. 1(A). The RF signalfalls from a first signal level LV11 to a second signal level LV12 whenthe light spot L1 passes through the end of the pit P1, and subsequentlymaintains the signal level LV12 until the light spot L1 has passed thepit P1 with itself lying across the pit P1, as shown in FIG. 1(B). Thisresults in a sum signal in which the signal level changes in response tothe lengths of the land and the pit P1 because the light spot L1 scansboth the land and the pit P1.

Thus, the signal level of the RF signal RF1 decreases during scanningdue to the interference between light reflected from the pit P1 andlight reflected from a reflecting surface (the land) located around thepit P1. This also occurs when a light spot L2 of a relatively small wavelength scans a pit P2 formed in an optical disc that has a higherrecording density than the compact discs.

Each time the light spot L2 formed by a laser beam of a relatively smallwave length enters the pit P2, an RF signal RF2, the signal level ofwhich changes from LV21 to LV22 in response to recorded information canbe obtained as shown in FIG. 2(B).

The light spot L2 formed by a laser beam of a relatively small wavelength can be converged on a small diameter compared to the light spotL1 formed by a laser beam of a relatively large wave length, so thewidth W2 of the pit P2 may be smaller than the width W1 of the pit P1.As a result, optical recording medium reproducing apparatuses using thelight spot L2 formed by a laser beam of a relatively small wave lengthdeal with a high recording density, while optical recording mediumreproducing apparatuses using the light spot L1 formed by a laser beamof a relatively large wave length cope with a low recording density.

If a high recording density optical recording medium reproducingapparatus is used to directly reproduce a compact disc (CD) designed tobe reproduced by a low recording density optical recording mediumreproducing apparatus, the diameter of the light spot L2 is smaller thanor equal to the width W1 of the pit P1, as shown in FIG. 3(A). In thiscase, light reflected from the land and light reflected from the pit P1interfere with each other when the light spot L2 enters and leaves thepit P1, whereas no interference occurs while the light spot L2 isscanning the pit P1 because it is totally included within the pit P1.The signal level of an RF signal RF3 changes from LV31 to LV32 only atboth ends of the pit P1, as shown in FIG. 3(B).

Although the signals shown in FIGS. 1(B) and 2(B) can be detected byintegral detection, the signal shown in FIG. 3(B) cannot be detected bysuch detection but requires differential detection. The differentialdetection, however, has a higher error rate than the integral detection.

This invention is proposed in view of the above points, and itsobjective is to provide an optical recording medium reproducingapparatus that performs reproducing operations using a light spot formedby a laser beam of a relatively small wave length and which cancompatibly reproduce low recording density optical recording media.

DISCLOSURE OF THE INVENTION

This invention provides an optical recording medium reproducingapparatus that reproduces information recorded on an optical recordingmedium with a plurality of pits formed along tracks based on therecorded information, comprising: a laser beam emitting means foremitting a laser beam; a focus control means for controlling thefocusing of the laser beam on the optical recording medium; and acontrol means for controlling the focus control means so as to increasethe spot diameter of the laser beam emitted onto the optical recordingmedium when the medium has a low recording density with pits relativelysparsely arranged compared to the case in which the medium has a highrecording density with pits relatively densely arranged.

Thus, when the optical recording medium mounted in the optical recordingmedium reproducing apparatus has a low recording density, this inventionenables the information recorded in the tracks of the mounted lowrecording density recording medium to be reliably reproduced as in highrecording density recording media, by using the control means to controlthe focus control means so as to increase the spot diameter of the laserbeam.

According to this invention, to provide control in such a way that thespot diameter of the laser beam will be increased, the control meanssupplies different focus bias values depending upon whether the opticalrecording medium has a high or a low recording density.

In addition, this invention comprises a light receiving means forreceiving a laser beam reflected from the optical recording medium; aservo error signal generating means for generating a servo error signalbased on an output signal from the light receiving means; a polaritydetecting means for detecting the polarity of the servo error signal;and a polarity selecting means for selecting the polarity of the servoerror signal based on an output signal from the polarity detectingmeans, thereby reliably enabling the optical recording medium to enter aservo operation state even when the polarity of the servo error signalfrom the optical recording medium differs from that of standard opticalrecording media.

In addition, this invention comprises a light receiving means forreceiving a laser beam reflected from the optical recording medium; aread (RF) signal generating means for generating a read (RF) signal forthe recorded information based on an output signal from the lightreceiving means; a tangential push-pull signal generating means forgenerating a tangential push-pull signal based on the output signal fromthe light receiving means; an error detecting means for detecting theerror conditions of the output signal from the light receiving means;and a selecting means for selectively outputting the read (RF) ortangential push-pull signal, wherein the control means controls theselecting means based on an output signal from the error detectingmeans. This constitution enables the selecting means to select thetangential push-pull signal (or a differential detection signal) inorder to switch to a state in which the recorded information can bereliably reproduced, when no read (RF) signal (or integral detectionsignal) of a sufficient magnitude of signal level can be obtained toprevent the recorded information from being completely reproduced.

Furthermore, this invention comprises a light receiving means forreceiving a laser beam reflected from the optical recording medium; aninput read (RF) signal generating means for generating an input read(RF) signal for the recorded information based on an output signal fromthe light receiving means; a tracking error generating means forgenerating a tracking error signal based on the output signal from thelight receiving means; an automatic level control means for providingcontrol so as to maintain a constant signal level of the input read (RF)signal and outputting an output read (RF) signal; and a normalizingmeans for normalizing the signal level of the tracking error signalbased on the signal level of the input read (RF) signal, therebyenabling the mounted optical recording medium to perform stable trackingoperations even when the medium has an extremely high or lowreflectance.

This invention thus employs an optical pickup that forms a light spot ofa small wave length in order to reproduce an optical recording mediumwith a high recording density of recorded information, and canautomatically set optimal reproducing conditions when a low recordingdensity optical recording medium is mounted instead of the current highrecording density optical recording medium, thereby enabling theimplementation of an optical recording medium reproducing apparatus thatcan compatibly reproduce various optical recording media.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A) and 1(B) are a schematic diagram and a signal waveform chart,respectively, describing the case in which a light spot formed by alaser beam of a large wave length reproduces pits with informationsparsely recorded therein.

FIGS. 2(A) and 2(B) are a schematic diagram and a signal waveform chart,respectively, showing a method for using a light spot formed by a laserbeam of a small wave length in order to reproduce pits with informationdensely recorded therein.

FIGS. 3(A) and 3(B) are a schematic diagram and a signal waveform chart,respectively, describing problems occurring when a light spot formed bya laser beam of a small wave length reproduces pits with informationsparsely recorded therein.

FIG. 4 is a block diagram showing the overall configuration of anoptical recording medium reproducing apparatus according to thisinvention.

FIG. 5 is a connection diagram showing the detailed constitution of amatrix circuit 13 in FIG. 4.

FIG. 6 is a connection diagram showing the detailed constitution of anasymmetry modulation degree detecting circuit 58 in FIG. 4.

FIG. 7 is a signal waveform chart showing reproduction signals forrecorded information 11T to 3T.

FIGS. 8(A) to 8(C) are a schematic diagram and a signal waveform chartdescribing a signal from each component of the asymmetry modulationdegree detecting circuit 58 in FIG. 6.

FIG. 9 is a flowchart showing a procedure for calibration.

FIG. 10 is a flowchart showing a subroutine RT1 for inputting a defaultfocus bias value in FIG. 9.

FIG. 11 is a flowchart showing a subroutine RT2 for determining thetracking polarity in FIG. 9.

FIG. 12 is a flowchart showing a subroutine RT3 for first focus biasvalue adjustment in FIG. 9.

FIG. 13 is a table showing the relationship between the absolute time inthe pregroove (ATIP) and the preset focus bias value processed in FIG.12.

FIG. 14 is a flowchart showing a subroutine RT4 for a second focus biasvalue adjustment in FIG. 9.

FIG. 15 is a flowchart showing the subroutine RT4 for the second focusbias value adjustment in FIG. 9.

FIG. 16 is a flowchart showing the subroutine RT4 for the second focusbias value adjustment in FIG. 9.

FIG. 17 is a flowchart showing a subroutine for a first selecting methodwhich is included in a subroutine RT5 for selecting an RF signal in FIG.9.

FIGS. 18(A) to 18(D) are a schematic diagram and signal waveform chartsdescribing an integrally and a differentially detecting methods.

FIG. 19 is a flowchart showing a subroutine RT52 for a third selectingmethod which is included in the subroutine RT5 for selecting an RFsignal in FIG. 9.

FIG. 20 is a flowchart showing a subroutine RT53 for the third selectingmethod which is included in the subroutine RT5 for selecting an RFsignal in FIG. 9.

FIG. 21 is a flowchart showing a subroutine RT54 for a fourth selectingmethod which is included in the subroutine RT5 for selecting an RFsignal in FIG. 9.

FIG. 22 is a flowchart showing a reproducing procedure.

BEST MODE FOR CARRYING OUT THE INVENTION

One embodiment of this invention is described below in detail withreference to the drawings.

(1) Overall Constitution

FIG. 4 generally shows an optical recording medium reproducing apparatusas 1 wherein a laser beam emitted from an optical pickup 5 forms a lightspot on a disc 4 as an optical recording medium rotated by a spindlemotor 3. The laser beam has a relatively small wave length that isoptimal for the reproduction of high recording density discs.

As described above in FIG. 2, the optical pickup 5 sequentially passesthrough a collimator lens 7, a beam splitter 8, and an objective lens 9,a laser beam from a laser diode 6 for generating a light beam of arelatively small wave length which reads high recording density discs,thereby forming irradiation light LA1, with which the disc 4 isirradiated. The optical pickup 5 also sequentially passes return lightLA2 through the objective lens 9, the beam splitter 8, and a lenticularlens 10, and the light is then divided through a grating (not shown)into a quarterly dividing detector 11A with detecting elements A, B, C,and D and two dividing detectors 11B and 11C with detecting elements Eand F, and G and H, respectively, and then enters the disc.

The detecting elements A, B, C, and D, and E, F, G, and H applydetection signals SA, SB, SC, and SD, SE and SF, and SG and SHcorresponding to the distribution of the light intensity over thefour-split detector 11A and the halving detectors 11B and 11C,respectively, which is generated by the return light LA2, to a matrixcircuit 13 via amplifying circuits 12A, 12B, 12C, and 12D, 12E and 12F,and 12G and 12H, respectively.

As shown in FIG. 5, the matrix circuit 13 has a focusing error signalforming circuit 13A for forming a focusing error signalFE(=(SA+SC)-(SB+SD)) based on astigmatism.

The matrix circuit 13 also has a tracking error signal forming circuit13B for forming a tracking error signalTE(=((SA+SD)-(SB+SC))-×((SE+SG)-(SF+SH))) using the detection signals SAand SD, and SB and SC from the detecting elements of the four-splitdetector 11A, A and D, and B and C, respectively, based on thedifferential push-pull method.

The tracking error signal may be formed as TE(=(SA+SD)-(SB+SC)) based onthe push-pull method.

The matrix circuit 13 also has a sum signal (RF signal) forming circuit13C for forming an RF signal RF(=SA+SB+SC+SD) using the detectionsignals from all the detecting elements A, B, C, and D, based on theintegral detecting method.

The matrix circuit 13 also has a tangential push-pull signal formingcircuit 13D for forming a tangential push-pull signalTPP(=(SA+SB)-(SC+SD)) using the detection signal from the two detectingelements A and B and the detection signal from the two detectingelements C and D in such a way that the light spot is divided into twoin the direction perpendicular to the light spot scanning direction,based on the differential detecting method.

The matrix circuit 13 also has a push-pull signal forming circuit 13Eused when a recordable optical disc with a pregroove (for example, aCD-R, CD-MO, or CD-E) is to be reproduced, in order to form a push-pullsignal PP(=(SA+SD)-(SB+SC)) as the difference between the detectionsignal from the two detecting elements A and D and the detection signalsfrom the two detecting elements B and C based on the push-pull method,in such a way that the light spot is divided along a parting lineextending along the light spot scanning direction.

In this case, the pregroove is provided beforehand in that region of therecordable optical disc in which data has not been recorded yet in orderto enable tracking. That is, the push-pull signal PP is used toreproduce recordable optical discs.

In the matrix circuit 13, the signal thus formed on the basis of thedetection signals SA, SB, SC, and SD from the detecting elements A, B,C, and D is used via a bus 14 for arithmetic processing in which acentral processing unit (CPU) 15 executes programs stored in a presetROM 16 using a RAM 17 as a work memory. Based on the results of thearithmetic operation, the optical pickup 5 is then controlled so as toperform a reading operation in optimal reproducing conditions for thedisc 4 mounted on a spindle motor 3.

The focusing error signal FE obtained from the focusing error signalforming circuit 13A (FIG. 5) in the matrix circuit 13 is delivered to adrive circuit 23 via a summing circuit 21 and a phase compensatingcircuit 22. This allows the provision of drive output to a focusingactuator 24 for the optical pickup 5 which causes the focusing errorsignal to have a negative focus bias value, resulting in the formationof a focusing servo loop.

In this focusing servo loop according to this embodiment, a focus biasvalue FB is provided to the summing circuit 21 from the CPU 15 via thebus 14 and a digital analog converting circuit 25. This enables theoptical pickup 5 to be positioned in a focus position corresponding tothe focus bias value FB.

The tracking error signal TE obtained from the tracking error signalforming circuit 13B (FIG. 5) in the matrix circuit 13 is provided to adrive circuit 30 via a switching input end A of a switching circuit 27,a divider 28, and a phase compensating circuit 29. This allows driveoutput to be applied to a tracking actuator 31 for the optical pickup 5,resulting in the formation of a tracking servo loop.

In addition, drive output from the drive circuit 30 is provided to adrive circuit 33 via a phase compensating circuit 32. This allows driveoutput to be supplied to a thread actuator 34 for the optical pickup 5,resulting in the formation of a thread servo loop.

In this embodiment, when a switching control signal S1 is provided fromthe CPU 15 via the bus 14, the switching circuit 27 delivers a trackingerror signal TE with its polarity inverted by an inverting circuit 35,to the divider 28 through the switching input end B. The polarity of thetracking error signal TE is thus inverted.

The divider 28 receives the RF signal RF from the RF signal formingcircuit 13C (FIG. 5) in the matrix circuit 13. This allows the signallevel of the tracking error signal TE to be normalized according to themagnitude of the signal level of the RF signal RF. Consequently, even ifthe mounted discs 4 have different reflectance, the amplitude of thetracking error signal TE will not be affected by these differences.

A phase control signal S2 is provided to the phase compensating circuit29 from the CPU 15 via the bus 14. This allows drive output for trackjump to be supplied to the tracking actuator 31 from the drive circuit30 upon track jump.

Upon track jump, a thread drive signal S5 is delivered to the phasecompensating circuit 32 from the CPU 15 via the bus 14. The phasecompensating circuit 32 then drives the thread actuator 34 via the drivecircuit 33 to cause the optical pickup 5 to perform a thread operation.

The RF signal obtained from the RF signal forming circuit 13C in thematrix circuit 13 is controlled by an AGC circuit 38 to a predeterminedgain and then provided to an RF signal demodulating circuit 39. The RFsignal demodulating circuit 39 demodulates reproduced data DATA1 fromthe RF signal RF as the results of integral detection, and externallysends the reproduced data DATA1 via the switching input end A of theswitching circuit 40 as reproduced DATA from the optical recordingmedium reproducing apparatus 1.

If when demodulating the reproduced data DATA1, the RF signaldemodulating circuit 39 cannot correct an error based on errorcorrection code (ECC) information provided for each frame, it sends outan error flag signal EF1 to the CPU 15 via the bus 14. This enables theCPU 15 to determine whether or not reproduced data DATA1 can beappropriately demodulated from the RF signal from the currently mounteddisc 4 based on the integral detecting method.

In this embodiment, the RF signal demodulating circuit 39 includes an RFreference clock generating circuit, and supplies a difference signal S3between the current RF reference clock signal and a clock signal for thedemodulated RF signal to a spindle servo circuit 41 to drive and controlthe spindle motor 3 so as to reduce the difference signal S3 to zero,resulting in the formation of a spindle servo loop.

The tangential push-pull signal TPP obtained from the tangentialpush-pull signal forming circuit 13D (FIG. 5) in the matrix circuit 13is delivered to an RF signal demodulating circuit 46 via a tangentialpush-pull signal processing circuit 45. The RF signal demodulatingcircuit 46 thus demodulates reproduced data DATA2 as the results ofdifferential detection, and externally sends the data DATA2 via theswitching input end B of the switching circuit 40 as reproduced DATAfrom the optical recording medium reproducing apparatus 1.

If when demodulating the reproduced data DATA2, the RF signaldemodulating circuit 46 cannot correct an error based on the ECCinformation provided for each frame, it sends out an error flag signalEF2 to the CPU 15 via the bus 14. This enables the CPU 15 to determinewhether or not reproduced data DATA2 can be appropriately demodulatedfrom the RF signal from the currently mounted disc 4 based on thedifferential detecting method.

When determining based on the error flag signal EF1 that the error uponthe demodulation of the reproduced data DATA1 obtained by the integraldetecting method is large, the CPU 15 supplies a switching controlsignal S4 to the switching circuit 40 via the bus 14 so as to cause thecircuit 40 to perform a switching operation. This allows the reproduceddata DATA2 obtained by the differential detecting method to be sent outvia the switching circuit 40 as reproduced data DATA from the opticalrecording medium reproducing apparatus 1.

Thus, if the data cannot be correctly reproduced from the results of theintegral detection, the results of the differential detection in placeof the integral detection can be sent out instead as the reproduceddata.

In this embodiment, the tracking error signal TE can be loaded in theCPU 15 via a tracking error amplitude detecting circuit 51, an analogdigital converting circuit 52, and the bus 14. The CPU 15 can providecontrol compatible with the disc 4 by identifying the tracking errorconditions of the optical pickup 5.

In addition, the amplitude of the RF signal RF is detected by an RFamplitude detecting circuit 55, and supplied to the CPU 15 via an analogdigital converting circuit 56 and the bus 14. This enables the CPU 15 todetermine the amplitude of the RF signal.

The RF signal RF is also provided to an asymmetry modulation degreedetecting circuit 58. Upon reading data 11T to 3T from the disc 4 asrecorded information, the asymmetry modulation degree detecting circuit58 supplies an asymmetry detection signal ASY to the CPU 15 via the bus14 indicating the asymmetry of the lengths of the land and the pit inthe RF signal, and sends out modulation degree detection signals M (11Tand 3T) for the longest data 11T and the shortest data 3T, respectively,to the CPU 15 via the bus 14.

As shown in FIG. 6, in the asymmetry modulation degree detecting circuit58, a differential circuit 58A differentiates the RF signal RF, and theoutput of the differential circuit 58A is then compared to a groundpotential by a comparing circuit 58B in order to obtain a rectangularwave signal S11 (FIG. 8(B)) with its signal level rising or falling whenthe RF signal of a data length of 3T to 11T (FIG. 7) reaches a peak or abottom level, respectively. An edge detecting circuit 58C furtherobtains a rising and a falling edge detection pulses S12A and S12Bcorresponding to the rising and the falling edge of the rectangular wavesignal S11, and provides it to a sampling pulse forming circuit 58D.

The sampling pulse forming circuit 58D then generates sampling pulsesS13A and S13B corresponding to the rising pulse S12A and the fallingpulse S12B. This allows sampling hold circuits 58E and 58F to sample andhold the signal level of the RF signal using a sampling pulse (FIG.8(C)) rising when the light spot passes the leading and the trailing endof a pit PX, as shown in FIG. 8(A). The sample hold value is accumulatedin a peak bottom hold circuit 58G.

The peak bottom hold circuit 58G thus has the peak and bottom values forthe shortest data 3T to the longest data accumulated therein. Amodulation degree asymmetry operation circuit 58H executes arithmeticoperations for the following equations (1) to (3) based on the peak andthe bottom values of the longest pit, for example, 11TTOP and 11TBTM andthe peak and the bottom values of the. shortest pit, for example, 3TTOPand 3TBTM. ##EQU1##

The modulation degree asymmetry operation circuit 58H thus determinesthe modulation degrees (11T and 3T) of the longest and the shortest pitsas well as the asymmetry and then sends them out as the output of theasymmetry modulation degree detecting circuit 58. The CPU 15 can thusconfirm the modulation degree and asymmetry of the reproducedinformation recorded on the currently mounted disc 4, based on the RFsignal.

Furthermore, the push-pull signal PP from the push-pull signal formingcircuit 13E (FIG. 5) in the matrix circuit 13 is delivered to anabsolute time in the pregroove (ATIP) data demodulating circuit 60. Theabsolute time in the pregroove data ATIP demodulated by the absolutetime in the pregroove (ATIP) data demodulating circuit 60 is supplied tothe CPU 15 via the bus 14.

Thus, when a recordable optical disc (referred to as a "CD-R") with apregroove according to the standard is mounted as the disc 4, the CPU 15can confirm the absolute time in the pregroove data ATIP inserted intothe pregroove according to a specified cycle (for example, a 10 fieldcycle).

In the above configuration, when either a high or a low recordingdensity optical disc is loaded as the disc 4, the central processingunit (the CPU) 15 of the optical recording medium reproducing apparatus1 sets reproducing conditions for the apparatus 1 by carrying out acalibration procedure RT0 in FIG. 9.

After entering the calibration procedure RT0, the CPU 15 first executesa subroutine RT1 to set as a focus bias default value an optimal focusbias value for a high recording density disc as the mounted disc 4.

If the data can then be reproduced correctly, the CPU 15 proceeds tostep SP0 to end the calibration procedure. Otherwise, the CPU 15determines that a low recording density disc has been loaded as the disc4, and proceeds to the next subroutine RT2.

In the subroutine RT2, the CPU 15 determines an optimal polarity of thetracking error signal for the mounted disc 4, and in the subsequentsubroutine RT3, sets the focus bias value to the preset focus bias valuespecified for the type of the mounted disc, as first focus bias valueadjustment processing.

If required, the CPU 15 then proceeds to a subroutine RT4 to carry outsecond focus bias adjustment processing, thereby adjusting the focusbias value according to the recording conditions of the informationrecorded on the mounted disc 4.

After the focus bias value adjustment has been finished, the CPU 15determines whether the integral or the differential detecting processingis used to demodulate the RF signal obtained from the mounted disc 4according to the conditions of the RF signal in a subroutine RT5, andthen ends the calibration procedure RT0 in step SP0.

Therefore, the CPU 15 can set optimal reproducing conditions dependingon the standards for the mounted disc 4 and the recording conditions ofthe recorded information in order to set reproducing conditions for theoptical recording medium reproducing apparatus 1 so that the apparatuscan compatibly reproduce various optical discs.

(2) Calibration Processing

In this embodiment, the CPU 15 executes the following processing in thesubroutines RT1 to RT5 constituting the calibration procedure RT0.

(2-1) Inputting a Default Focus Bias Value (RT1)

After entering the subroutine RT1 for inputting a default focus biasvalue in FIG. 9, as shown in FIG. 10, in step SP1, the CPU 15 first setsas a focus bias value FB a high recording density focus bias value DFHthat is most suited to the reproduction of high recording density discs.

The default high recording density focus bias value DFH is stored in thepreset ROM 16 as the initial value set on the program. The CPU 15supplies the default high recording density focus bias value DFH fromthe bus 14 via the digital analog converting circuit 25 to the summingcircuit 21 constituting the focus servo loop, as the focus bias value.

The CPU 15 subsequently proceeds to step SP2 to turn on the focus servoloop, the tracking servo loop, and the spindle servo loop, and thefocusing actuator 24 then controls the optical pickup 5 to a focusposition corresponding to the default high recording density focus biasvalue DFH.

Under these conditions, the CPU 15 proceeds to step SP3 to supply the RFsignal RF obtained from the RF signal forming circuit 13C in the matrixcircuit 13, to the RF signal demodulating circuit 39 via the AGC circuit38. The RF signal demodulating circuit 39 thus decodes a frame N1 of thereproduced data DATA1 in order to detect the error conditions of thedata DATA1 on a frame basis based on the error correction codes ECCcontained therein, and supplies the error flag signal EF1 to the CPU 15via the bus 14. This causes the CPU 15 to count the number of times whenthe error flag has been generated.

The CPU 15 subsequently proceeds to step SP4 to determine whether or notthe number of error flags is larger than a specified threshold Th.

The threshold Th is a value used to determine that the currently mounteddisc 4 does not have a high recording density (that is, the disc 4 doesnot require scanning with a light spot formed by a laser beam of a smallwave length). If a negative result is obtained in step SP4, this meansthat the currently mounted disc 4 has a high recording density. In thiscase, the CPU 15 returns to step SP0 of the main routine (FIG. 9) fromstep SP5 to end the calibration procedure RT0.

If a positive result is obtained in step SP4, however, this means thatthe modulated data based on the RF signal RF obtained from the matrixcircuit 13 has caused a larger number of error flags than expected forhigh recording density discs to be transferred as the error flag signalsEF1. The CPU 15 thus determines that the currently mounted disc 4 has alow recording density, and then returns to the subroutine RT2 of themain routine (FIG. 9) from step SP6.

Thus, the subroutine RT1 for inputting a default focus bias valueexecutes calibration in such a way that the RF signal RF is read fromthe disc 4 with the focus bias value initialized so as to form anoptimal light spot L2 for the reproduction of a pit P2 of a width W2(FIG. 2) required for high recording density discs. Thus, in step SP4,the CPU 15 determines whether the disc 4 has a high or a low recordingdensity, and in the case of a high recording density disc, sets anoptimal focus bias value for the reproduction of the disc.

Otherwise, the CPU 15 subsequently carries out the subroutines RT2 toRT5 of the main routine (FIG. 9).

(2-2) Determining the Tracking Polarity (RT2)

Upon entering the subroutine RT2 for determining the tracking polarityfrom the subroutine RT1 for inputting a default focus bias value in themain routine (FIG. 9), the CPU 15 turns on the focus servo loop, thetracking servo loop, and the spindle servo loop in step SP11 in FIG. 11.The CPU 15 then sets the focus bias value FB to the default bias valueDFL for low recording density discs in step SP12.

The CPU 15 subsequently proceeds to step SP13 to provide the switchingcontrol signal S1 via the bus 14 to the switching circuit 27 in thetracking servo loop to cause the circuit 27 to switch to the switchinginput end A. This provides control in such a way that the tracking errorsignal TE sent out from the tracking error signal forming circuit 13B inthe matrix circuit 13 is directly passed to the divider 28.

Under these conditions, when a low recording density optical disc ismounted as the disc 4, the CPU 15 uses the RF signal demodulatingcircuit 39 to demodulate the RF signal RF from the RF signal formingcircuit 13C in the matrix circuit 13 in order to count for N2 frames thenumber of error flags detected for each frame of the reproduced dataDATA1 based on the error correction codes ECC added to the frame in thesubsequent step SP14, and determines the count of error flags M0 in thenext step SP15.

When, however, an optical disc with a pregroove (a CD-R) is mounted asthe disc 4, the CPU 15 uses the absolute time in the pregroove (ATIP)data demodulating circuit 60 to demodulate the push-pull signal PP fromthe push-pull signal forming circuit 13E in the matrix circuit 13 inorder to count for N2 frames the number of error flags detected for eachframe of the reproduced data DATA1 based on the error correction codesCRC added to the frame in step SP14, and determines the count of errorflags M0 in the next step SP15.

The CPU 15 subsequently delivers the switching control signal S1 to theswitching circuit 27 to switch the circuit 27 to the switching input endB in step SP16. Consequently, the tracking error signal TE the polarityof which is inverted by the inverting circuit 35 is passed to thedivider 28 via the switching input end B. This allows the polarity ofthe tracking error signal TE to be inverted.

Under these conditions, as in step SP14, the CPU 15 counts for N2 framesthe number of error flags detected for each frame based on the errorcorrection codes ECC in the RF signal or the error correction codes CRCin the absolute time in the pregroove (ATIP) data in Step S17, anddetermines the count of error flags M1 based on the results of the countin step SP18.

The CPU 15 subsequently proceeds to step SP19 to determine whether ornot the count M0 is smaller than the count M1, and if the result ispositive, sets the switching circuit 27 to the switching input end A instep SP20, and then returns to the subroutine RT3 of the main routine(FIG. 9) from step SP21.

If, however, the result is negative in step SP19, the CPU 15 sets theswitching circuit 27 to the switching input end B in step SP19, and thenreturns to the subroutine RT3 of the main routine (FIG. 9) from stepSP21.

In this manner, the CPU 15 executes the subroutine RT2 for determiningthe tracking polarity in order to set to a polarity that reduces thenumber of error flags in the reproduced data DATA1, the polarity of thetracking error signal that must be fed back to the tracking servo loopwhen an optimal default focus bias value for low recording densityoptical discs has been supplied. This enables the polarity of thetracking error signal to be set so as to feed back to the tracking servoloop a tracking error signal appropriate for the currently mounted lowrecording density optical disc 4.

For write once type optical discs (for example, CD-Rs) that enable datato be reproduced as in pits in optical discs for reproduction only byirradiating a pigment with a laser beam to vary the conditions of thepigment, the polarity of the tracking error signal is determined by therelationship between the wave length of the laser beam and the depth ofthe grooves. Thus, although the polarity of the tracking error may beinverted if a laser for high recording density recording media, that is,a laser of a small wave length is used, the above processing provides anappropriate polarity of the tracking error.

(2-3) First Focus Bias Value Adjustment (RT3)

Upon entering the subroutine RT3 for first focus bias value adjustmentof the main routine (FIG. 9), the CPU 15 turns on the focus servo loop,the tracking servo loop, and the spindle servo loop in step SP31, asshown in FIG. 12. In step SP32, the CPU 15 provides the thread drivesignal S5 via the bus 14 to the phase compensating circuit 32 for thethread actuator 34 in order to cause the optical pickup 5 to seek to thelead in area of the storage area of the currently mounted disc 4. TheCPU 15 subsequently reads the absolute time in the pregroove (ATIP)information reproduced from the Table of Contents (TOC) area of theleadin area in step SP33. It then determines in step SP34 whether or notthere are matching time information ATIP.

The positive result in step SP34 means that the currently mounted disc 4is a recordable optical disc in which optical pits containing recordedinformation are formed in the pregroove (for example, a CD-R). The CPU15 then proceeds to step SP35 to set a preset value corresponding to theabsolute time in the pregroove information ATIP as the focus bias value(that is, to rewrite the preset value DFL (step SP12 in FIG. 11)recorded in the drive circuit 23 in the focusing servo loop).

The CPU 15 thus ends the subroutine for first focus bias valueadjustment, and returns to the subroutine RT5 of the main routine (FIG.9) in step SP36.

These discs with the absolute time in the pregroove information ATIP(CD-Rs) include in the ATIP, absolute time in the disc information andmanufacturer information indicating disc manufacturers.

The preset ROM 16 of the optical recording medium reproducing apparatus1 contains preset information for the focus bias value, as shown in FIG.13. Specifically, ATIP information showing disc manufacturers and thepreset focus bias values corresponding to each disc manufacturer arestored in a table. Thus, when the table contains ATIP informationmatching the ATIP information obtained in step SP33, the focus biasvalue corresponding to this ATIP information can be set by reading itfrom the table.

The preset focus bias value that has been written to the preset ROM 16in correspondence to the device manufacturer of the currently mounteddisc 4 can thus be set as the focus bias value in order to set anoptimal focus bias value for the currently mounted optical disc.

If the result is negative in step SP34, the currently mounted disc doesnot have a pregroove and is used only for reproduction, or the disc isof a write once type but has no information on disc manufacturers presetin the preset ROM 16. The CPU 15 then returns to the subroutine RT4 ofthe main routine (FIG. 9) from step SP37.

When the currently mounted disc 4 is a recordable disc with a pregroove(a CD-R), the first focus bias value adjustment is FIG. 12 enables thepreset focus bias value recorded on the disc (the CD-R) to be used toset the optical pickup 5 in an optimal focus bias position.

(2-4) Second Focus Bias Value Adjustment (RT4)

When the result is negative in step SP34 of the subroutine RT3 for thefirst focus bias value adjustment and the CPU 15 thus returns to thesubroutine RT4 from step SP37, the CPU 15 enters a second focus biasvalue adjustment in FIGS. 14 to 16. In step SP40, the CPU 15 first setsas the focus bias value a default focus bias value FBD representing anoptimal focus bias value when the currently mounted disc 4 has a lowrecording density.

The CPU 15 also sets at zero a loop count value X representing thenumber of loop operations within the processing routine RT4. It proceedsto the next step SP41 to turn on the focusing servo loop, the trackingservo loop, and the spindle servo loop.

In the subsequent step SP42, the CPU 15 uses the RF signal amplitudedetecting circuit 55 to detect the amplitude of the RF signal RFobtained from the RF signal forming circuit 13C in the matrix circuit13, and stores the results of the detection in the RAM 17 as the RFsignal amplitude value RFN via the analog digital converting circuit 56and the bus 14. In the subsequent step SP43, the CPU 15 determineswhether or not the stored RF signal amplitude value RFN exceeds athreshold A1.

A positive result in this step means that the currently set focus biasvalue FB(=FBD) is appropriate for the recorded information to be readfrom the currently mounted low density disc 4. The CPU 15 then proceedsto step SP44 to store the currently set focus bias value FB in the RAM17 as a focus bias value FBRF(X) that is effective when the number ofloop operations is X.

The CPU 15 then passes to step SP45 to determine whether or not the RFsignal amplitude value RFN stored in step SP42 is larger than a maximumRF signal amplitude value RFN stored in the RAM 17, and if so, passes tostep SP46 to store the RF signal amplitude value larger than the maximumRF signal amplitude value RFM in the RAM 17 as a new maximum RF signalamplitude value RFM. The CPU 15 subsequently stores the effective focusbias value FBRF(X) stored in step SP44, in the RAM 17 as a maximum RFfocus bias value in step SP47.

In the determination in step SP45, the initial maximum RF signalamplitude value is assumed to be zero.

In this manner, the CPU 15 leaves in the RAM 17 a maximum RF focus biasvalue FBRFMAX that results in the maximum RF signal amplitude when thetracking servo loop is turned on and when the number of loop operationsis X.

In the next step SP48, the CPU 15 turns the tracking servo off with thefocusing servo turned on. It then stores as a detected tracking errorsignal value TEN the amplitude of the tracking error signal TE obtainedfrom the tracking error signal forming circuit 13B in the matrix circuit13 in step SP49. It then determines in step SP50 whether or not thedetected tracking error signal value TEN is larger than a threshold A2.

A positive result in this step means that the current focus bias valueis valid. The CPU 15 then proceeds to step SP51 to store the currentfocus bias value FB in the RAM 17 as the effective focus bias valueFBTE(X), and determines in step SP52 whether or not the detectedtracking error signal value TEN is larger than a maximum tracking errorsignal amplitude value TEM.

A positive result in this step means that the amplitude value of thecurrently detected tracking error signal TE has the maximum value. TheCPU 15 then stores the amplitude value of the currently detectedtracking error signal TE in the RAM 17 as the maximum tracking errorsignal amplitude value TEM in step SP53, and also stores the effectivefocus bias value FBTE(X) stored in step SP51, in the RAM 17 as a maximumtracking error focus bias value FBTEMAX.

In the determination in step SP52, the maximum tracking error signalamplitude value TEM is initially set at zero.

The CPU 15 thus loads the maximum tracking error signal value in the RAM17 whenever the tracking servo loop is turned off.

The CPU 15 subsequently passes to step SP55 to confirm that the numberof loop operations X is smaller than a maximum number of loop operationsXm, and increments this number by 1 in step SP56. It then sets a newfocus bias value FB by adding a constant value C to it in step SP57, andthen returns to the above step SP41. It then repeats the same loopoperation processing for the number of loop operations X+1.

While in step SP57, the number of loop operations X is sequentiallyincremented by the constant value C until it reaches its maximum valueXm, the CPU 15 stores in the RAM 17 the focus bias values FBRF(X) andFBTE(X) that are effective when tracking is turned on and when it isturned off, respectively, in steps SP44 and SP51, and also stores in theRAM 17 the maximum RF signal amplitude value RFM and the maximumtracking error signal amplitude value TEM which are obtained when thetracking is turned on and when it is turned off, respectively, in stepsSP46 and SP53.

That is, by repeating the loop operation processing from step SP40 toSP57, the group of effective focus bias values FBRF(X) and FBTE(X)obtained from the respective loop operations are stored in the RAM 17,and within the group of effective focus bias values, the RF and thetracking error signal amplitude values obtained when the RF signal RFand tracking error signal TE have maximum values are left in the RAM 17as the maximum RF signal amplitude value RFM and the maximum trackingerror signal amplitude value TEM, respectively.

In the above loop operations, a negative result in steps SP43 to SP50means that the detected RF signal value RFN and the detected trackingerror signal value TEN which are detected in steps SP42 and SP49,respectively, are invalid. In this case, the CPU 15 skips the processingin steps SP44 to SP47 and SP51 to SP54, and proceeds to steps SP48 andSP55 from steps SP43 and SP50, respectively.

A negative result in steps SP45 and SP52 means both the detected RFsignal amplitude value RFN and the detected tracking error signalamplitude value TEN which are obtained when the effective focus biasvalues FBRF(X) and FBTE(X) are not the maximum value. In this case, theCPU 15 passes to steps SP48 and SP55 without executing the processing insteps SP46 and SP47, and SP53 and SP54, respectively.

In the loop operation processing in steps SP41 to SP57, the CPU 15sequentially increments the focus bias value FB by the constant value C,while in the loop operation processing in steps SP60 and subsequentsteps, it sequentially decrements this value by the constant value Ceach time a single loop operation is performed.

That is, in steps SP60 to SP67, the CPU 15 stores in the RAM 17 thegroup of effective focus bias values FBRF(X) and the maximum RF signalamplitude value RFM and the maximum RF focus bias value FBRFMAX, asdescribed in the above steps SP40 to SP47.

In steps SP68 to SP74, the CPU 15 stores the group of effective focusbias values FBTE(X) obtained when the tracking servo is turned off andwhen the focusing servo is turned on, as well as the maximum trackingerror signal amplitude value TEM, as described in the above steps SP48to SP54.

After finishing this processing, the CPU 15 passes to step SP80 todetermine a group of comprehensive effective detected focus bias valuesFBOK(X) assuming that the groups of effective focus bias values FBRF(X)and FBTE(X) obtained in steps SP44 and SP51, and SP64 and SP71,respectively, are within effective ranges above the thresholds A1 andA2, respectively.

The CPU 15 subsequently proceeds to step SP81 to determine optimal focusbias values FB1, FB2, and FB3 based on three determination criteria.

A first determination criterion is that the CPU 15 determines as a firstoptimal focus bias value FB1 one of the comprehensive effective detectedfocus bias values FBOK(X) which is closest to the maximum detected RFfocus bias value FBRFMAX.

A second determination criterion is that the CPU 15 determines as asecond optimal focus bias value FB2 one of the comprehensive effectivedetected focus bias values FBOK(X) which is closest to the maximumdetected tracking error focus bias value FBTEMAX.

A third determination criterion is that the CPU 15 determines as a thirdoptimal focus bias value FB3 the central value of the comprehensiveeffective detected focus bias values FBOK(X).

The second focus bias value adjustment ends when the first, second, andthird optimal focus bias values FB1, FB2, and FB3 are determined in theabove manner, and the CPU 15 then and returns to the subroutine RT5 ofthe main routine (FIG. 9) from step SP82.

When a low recording density disc is mounted as the disc 4, by executingthe second focus bias value adjustment in FIGS. 14 to 16, the CPU 15increments the focus bias value by the constant value C to determine therange of effective focus bias values within which the RF signal can havea sufficient magnitude to be detected when the tracking servo loop isturned on or off and within which the amplitude of the tracking errorsignal can also have a sufficient magnitude to be detected. It thendetermines the optimal focus bias values FB1, FB2, and FB3 from thegroup of effective focus bias values. The CPU 15 can thus reliably set afocus bias value that enables the obtention of the RF and the trackingerror signals of sufficient amplitudes to reproduce the informationrecorded on the currently mounted low recording density disc 4.

(2-5) Selecting an RF Signal (RT5)

In the subroutine for selecting an RF signal (RT5), the CPU 15determines whether the switching circuit 40 is to be set to theswitching input end A or B by determining whether the data DATA1demodulated by the RF signal modulating circuit 39 or the reproduceddata DATA2 demodulated by the RF signal demodulating circuit 46 isoptimal in terms of the error rate, the modulation degree, and theasymmetry value.

Upon entering the procedure RT5 for selecting an RF signal, the CPU 15first executes a first selecting processing routine RT51 (FIG. 17).

In step SP91 in which the integral detection method is used to reproducethe reproduced data DATA1, the CPU 15 counts for N3 frames error flagsignals EF1 detected by the RF signal demodulating circuit 39 on a framebasis to obtain the number of error flags E0.

The CPU 15 subsequently proceeds to step SP92 in which the differentialdetection method is used to reproduce the reproduced data DATA2, the CPU15 counts for N3 frames error flag signals EF2 detected by the RF signaldemodulating circuit 46 on a frame basis to obtain the number of errorflags E1.

In the next step SP93, the CPU 15 determines whether or not the numberof error flags E0 is smaller than the number of error flags E1.

A positive result in this step means that a smaller number of errorflags can be obtained from the currently mounted disc 4 by using theintegral detecting method to demodulate the reproduced data DATA1. TheCPU 15 then passes to step SP94 to add 1 to an A count value A(initially set to zero), and then proceeds to step SP95.

A negative result in step SP93, however, means that for the currentlymounted disc 4, a smaller number of error flags can be obtained when thereproduced data DATA2 is demodulated by the differential detectionmethod. The CPU 15 then passes to step SP96 to add 1 to an B count valueB (initially set to zero), and then proceeds to step SP95.

In this manner, the CPU 15 determines in terms of the characteristics ofthe error rate whether the integral or the differential detection methodis optimal, and stores the count value A or B plus 1 as the result ofdetermination.

As shown in FIG. 18(A), when the currently mounted disc 4 has datarecorded in pits P1 of a width W1 required for low recording densitywhereas the optical pickup 5 uses a laser beam of a small wave length toform a light spot L2 of a small diameter, the RF signal obtained by theRF signal forming circuit 13C in the matrix circuit 13 using theintegral detection method is subjected to changes in its level as shownby the solid and the broken lines in FIG. 18(B) only when the light spotL2 enters and leaves the pit P1.

Consequently, the recorded information cannot be reproduced using theintegral detection as described above in FIG. 3(B). In FIG. 18(A),however, the tangential push-pull signal is as shown in FIG. 18(C), anddifferentiating this signal results in the signal shown in FIG. 18(D).The edge position of the pit can be detected from the signal in FIG.18(D), so the recorded information can be reproduced.

That is, even if the adjustment of the focus bias value is insufficientfor the reproduction of a low recording density recording medium and thecondition shown in FIG. 1(A) cannot be achieved, the recordedinformation can be reproduced by switching to the differentialdetection.

Next, in step SP95, the CPU 15 detects the modulation degree of data 11Tor 3T according to Equations (1) and (2) described above, using thedetection outputs M (11T and 3T) obtained by the asymmetry modulationdegree detecting circuit 58 and based on the RF signal RF obtained bythe RF signal forming circuit 13C in the matrix circuit 13, and in thenext step SP97, determines whether or not the demodulation degree ishigher than or equal to the threshold.

A positive result in this step means that the focus bias value can beadjusted accurately whether the disc has a high or a low recordingdensity and that the integral detection enables the data to besubstantially sufficiently reproduced.

The CPU 15 then proceeds to step SP98 to add 1 to the A count value A,and then passes to step SP99.

A negative result in step SP97, however, means that the focus bias valuecannot be reliably adjusted whether the disc has a high or a lowrecording density and that the integral detection does not enable thedata to be substantially sufficiently reproduced.

The CPU 15 then proceeds to step SP100 to add 1 to the B count value,and then passes to step SP99.

In this manner, the CPU 15 determines in terms of the characteristics ofthe demodulation degree whether the integral or the differentialdetection method is optimal, and stores the count value A or B plus 1 asthe results of determination.

In step SP99, the CPU 15 detects the asymmetry value ASY for the landand the pit according to Equation (3), using the detection output ASYobtained by the asymmetry demodulation degree detecting circuit 58 andbased on the RF signal RF obtained by the RF signal forming circuit 13Cin the matrix circuit 13, and in the next step SP101, determines whetherthe asymmetry value ASY is within a predetermined range.

A positive result in this step means that the asymmetry of the land andthe pit has a sufficient value for the data to be reproduced. The CPU 15then proceeds to step SP102 to add 1 to the count value A, and thenpasses to step SP103.

A negative result in step SP101, however, means that the results of theintegral detection do not provide a symmetry required to reproduce gooddata whether the disc has a high or a low recording density. The CPU 15then proceeds to step SP104 to add 1 to the count value B, and thenpasses to step SP103.

In this manner, the CPU 15 determines in terms of the asymmetry of theland and the pit whether the integral or the differential detectionmethod is optimal, and stores the count value A or B plus 1 as theresults of determination.

Next, in step SP103, the CPU 15 determines whether or not the countvalue A is larger than the count value B. If the result is positive, theCPU 15 determines that the integral detecting method is optimal, setsthe switching circuit 40 to the switching input end A in step SP105, andthen returns to step SP0 from step SP106.

A negative result in step SP103, however, means that the differentialdetecting method is optimal. The CPU 15 then sets the switching circuit40 to the switching input end B in step SP107, and then returns to stepSP0 from step SP106.

According to a method 1 in the subroutine RT51 for selecting an RFsignal in FIG. 17, by executing the processing in steps SP91 to 93, SP95and SP97, and SP99 and SP101, the CPU 15 can store as the cumulativeresults of the count A or B, respective optimal detection methods interms of the number of error flags, modulation degree, and asymmetryvalue for the land and the pit for the reproduced data obtained by theintegral and the differential detecting methods, thereby reliablyselecting a comprehensively optimal detection method.

Only a part of the selecting processing routine RT51 (FIG. 17) can becarried out to process the procedure RT5 for selecting an RF signal.

That is, as a second method for processing the selecting procedure RT5,the CPU 15 enters the selecting processing routine RT52, and in stepsSP111 to SP113, executes the same processing as in steps SP91 to SP93 ofthe processing procedure in FIG. 17, as shown in FIG. 19.

When determining from a positive result in step SP113 that a smallernumber of error flags can be obtained from the currently mounted disc 4by using the integral detecting method to reproduce the reproduced data,the CPU 15 sets the switching circuit 40 to the switching input end A instep SP114, and then returns to step SP0 (FIG. 9) from step SP115.

Conversely, when determining from a negative result in step SP113 that asmaller number of error flags can be obtained from the currently mounteddisc 4 by using the differential detecting method to reproduce thereproduced data, the CPU 15 sets the switching circuit 40 to theswitching input end B in step SP116, and then returns to step SP0 (FIG.9) from step SP115.

The second method comprising the selecting processing subroutine RT52 inFIG. 19 serves to implement an optical recording medium reproducingapparatus that select either the use of the integral detecting method toreproduce the reproduced data DATA1 or the use of the differentialdetecting method to reproduce the reproduced data DATA2 so as to reducethe number of error flags.

Next, as a third method for processing the selecting procedure RT5, theCPU 15 enters the selecting processing routine RT53, and in steps SP121and SP122, executes the same processing as in steps SP95 and SP97 of theprocessing procedure in FIG. 17, as shown in FIG. 20.

When determining from a positive result in step SP122 that an RF signalwith a sufficient modulation degree can be obtained from the currentlymounted disc 4 by using the integral detecting method to reproduce thereproduced data, the CPU15 sets the switching circuit 40 to theswitching input end A in step SP123, and then returns to step SP0 (FIG.9) from step SP124.

Conversely, when determining from a negative result in step SP122 thatan RF signal with a sufficient modulation degree can be obtained fromthe currently mounted disc 4 by using the differential detecting methodto reproduce the reproduced data, the CPU 15 sets the switching circuit40 to the switching input end B in step SP125, and then returns to stepSP0 (FIG. 9) from step SP124.

In this manner, based on whether or not the pits of the currentlymounted disc 4 can be detected at a sufficient modulation degree, thethird method comprising the selecting processing subroutine RT53 in FIG.20 enables the recorded data to be substantially sufficiently reproducedby using the integral detecting method to reproduce the reproduced dataDATA1 if the pits can be detected at a sufficient modulation degree andotherwise using the differential detecting method. If the pit cannot bedetected with a sufficient modulation degree, the recorded data can besubstantially sufficiently reproduced by using the differentialdetecting method.

Next, as a fourth method for processing the selecting procedure RT5, theCPU 15 enters the selecting processing routine RT54, and in steps SP131and SP132, executes the same processing as in steps SP99 and SP101 ofthe processing procedure in FIG. 17, as shown in FIG. 21.

When determining from a positive result in step SP132 that an RF signalwith a sufficient asymmetry value can be obtained from the currentlymounted disc 4 by using the integral detecting method to reproduce thereproduced data, the CPU 15 sets the switching circuit 40 to theswitching input end A in step SP133, and then returns to step SP0 (FIG.9) from step SP134.

Conversely, when determining from a negative result in step SP132 thatan RF signal with a sufficient asymmetry value can be obtained from thecurrently mounted disc 4 by using the differential detecting method toreproduce the reproduced data, the CPU 15 sets the switching circuit 40to the switching input end B in step SP135, and then returns to step SP0(FIG. 9) from step SP134.

In this manner, the fourth method comprising the selecting processingroutine RT54 in FIG. 21 selects either the data obtained by the integraldetecting method or the data obtained by the differential detectingmethod based on whether or not the asymmetry value ASY is appropriate.

(2-6) Summary of Calibration Processing

As described above, the CPU 15 carries out the calibration processingprocedure RT0 in FIG. 9 and ends it when the number of error flagsobtained is smaller than the threshold if in the subroutine RT1 forinputting a default focus bias value, the CPU sets as the initial valuean optimal default focus bias value for a light spot of a small wavelength required for a high recording density, because in this case, thecurrently mounted disc 4 has a high recording density.

If, however, the number of error flags is larger than or equal to thethreshold when the default focus bias value is initialized, the CPU 15determines that the mounted disc 4 has a low recording density, andexecutes the routine RT2 for determining the tracking polarity (FIG.11). This allows the polarity of the tracking error signal obtained fromthe currently mounted disc 4 to be set so as to reduce the number oferrors. This in turn enables reproducing conditions to be set so as toadequately control tracking according to the characteristics of themounted disc 4.

Under these conditions, the CPU 15 carries out the subroutine RT3 foradjusting the focus bias value (FIG. 12) to determine whether themounted disc 4 includes the absolute time in the pregroove (ATIP)information. If so, the CPU 15 sets an optimal focus bias value for thedisc with a pregroove.

As a result, if a disc with a pregroove is mounted as the disc 4, thefocus bias value can be set so as to obtain a light spot of a diametercompatible with this disc.

If, however, a disc without a pregroove is mounted as the disc 4, theCPU 15 executes the second subroutine RT4 for adjusting the focus biasvalue (FIGS. 14 to 16) in order to set the focus bias value so as toobtain a light spot diameter required to reproduce the mounted lowrecording density disc 4 with a light spot formed by a laser beam of asmall wave length.

The CPU 15 can thus set an optimal light spot diameter for the pit widthof a low recording density disc if such a disc is mounted.

Furthermore, the CPU 15 executes the selecting processing subroutine RT5(FIGS. 17 to 21) to set reproducing conditions in which the reproduceddata obtained by the differential detecting method is used if thereproduced data obtained by the integral detecting method does notprovide higher performance than the reproduced data DATA2 obtained bythe differential detecting method in terms of the number of error flags,the modulation degree of the data, and the asymmetry value for the landand the pit.

Therefore, this apparatus can execute calibration so as to automaticallyset reproducing conditions in which practically sufficiently appropriatereproduced data can be obtained not only when high recording densitydiscs are mounted but also when low recording density discs are loadedas the disc 4.

(3) Reproducing Recorded Information

The CPU 15 carries out the calibration processing in FIG. 9 to optimizethe reproducing conditions of the optical recording medium reproducingapparatus 1 according to the type of the mounted disc 4. Whenreproduction is requested by using an operation input key 70, the CPU 15executes the reproducing procedure RT10 shown in FIG. 22 to reproducethe information recorded on the mounted disc 4.

Upon entering the reproducing procedure RT10, the CPU 15 reads theaddress that the optical pickup 5 is accessing in step SP151, anddetermines in step SP152 whether or not a track jump is required.

Here, obtaining a negative result means the optical pickup 5 isaccessing the target address.

The CPU 15 then determines that a seek operation has been finished,proceeds to step SP153 to read the information recorded on the mounteddisc 4, and then passes to step SP154 to end the reproducing procedureRT10.

A positive result in step SP152, however, means that a track jump isrequired.

In this case, the CPU 15 proceeds to step SP155 to provide the phasecontrol signal S2 to the phase compensating circuit 29 in the trackingservo loop in order to instruct the circuit to initiate a track jump. Itdetermines in step SP156 whether the apparatus is in a mode that allowsthe switching of the reproducing conditions.

The optical recording medium reproducing apparatus 1 can select either aswitching mode that allows the focus bias value to be switched dependingupon whether a read or a track jump is required or a fixed mode thatdoes not allow the switching of the focus bias value.

A positive result in step SP156 means that the apparatus is in theswitching mode. The CPU 15 then passes to step SP157 to set as the focusbias value FB the optimal focus bias value FB2 determined as the seconddetermined condition in step SP81 of the subroutine RT4 for the secondfocus bias value adjustment (FIGS. 14 to 16). It then provides thisvalue to the summing circuit 21. This enables the diameter of the lightspot of the optical pickup 5 to be increased to obtain a tracking errorsignal TE with the largest amplitude from the mounted disc 4, resultingin practically sufficient tracking operations. After finishing thesetting of the focus bias value in step SP157, the CPU 15 passes to stepSP158 to wait for the track jump to end.

A negative result in step SP156, however, means that the apparatus is inthe fixed mode. The CPU 15 then proceeds to step SP158 to wait for thetrack jump to end.

Once the track jump of the optical pickup 5 has been finished, the CPU15 proceeds to step SP159 to determine whether the apparatus is in theswitching mode. If the result is positive, the CPU 15 sets as the focusbias value FB the optimal focus bias value FB1 determined as the firstdetermined condition in step SP81 of the subroutine RT4 for the secondfocus bias value adjustment in step SP160, and then reads the address instep SP161. The CPU 15 passes to step SP162 to determine whether thetarget address has been reached.

Since the focus bias value has been set to the focus bias value FB1 instep SP160, the light spot of the optical pickup 5 is set so that the RFsignal will have the largest amplitude. This ensures that the addresscan be read in step SP161.

In step SP161, when a disc used only for reproduction is mounted as thedisc 4, the CPU 15 can read the address from the reproduced data DATA1reproduced by the RF signal demodulating circuit 39. In addition, when awrite once disc with a pregroove (a CD-R) is mounted as the disc 4, itcan read the address from the absolute time in the pregroove ATIP dataobtained by the absolute time in the pregroove (ATIP) data modulatingcircuit 60.

A negative result in step SP159, however, means that the apparatus is inthe fixed mode. In this case, instead of setting the focus bias value FBin step SP160, the CPU 15 skips this step and passes to step SP162.

In step SP162, when determining that the target address has not beenreached yet, the CPU 15 returns to the above step SP155.

If, however, the result is positive in step SP162, the CPU 15 determinesthat a seek operation has been finished, and executes the read operationin the above step SP153. The CPU 15 then ends the reproducing procedurein step SP154.

Since the reproducing procedure RT10 in FIG. 22 sets different optimalfocus bias values depending upon whether a track jump or reproduction isto be executed out based on the reproducing conditions set by thecalibration procedure RT0 (FIG. 9), both track jump operations andreproduction can be reliably carried out whether the disc has a high ora low recording density. For high recording density discs, thereproducing procedure in FIG. 22 can be coped with by storing thedefault focus bias value DFH for reproduction set in step SP1, in theROM 16 as FB1 beforehand and also storing a focus bias value for a trackjump in the ROM 16 as FB2 beforehand.

(4) Other Embodiments

(4-1) Although the above embodiments have been described in conjunctionwith the application of a compact disc as the disc 4 that is an opticalrecording medium, this invention is not limited to this aspect, but maybe widely applicable to various media from which the optical pickup canread the recorded information.

(4-2) Although the above embodiments have been described in conjunctionwith the use of a compact disc as the optical recording medium 1, thisinvention is not limited to this aspect, but may be widely applicable tothose discs which the optical pickup can reproduce.

INDUSTRIAL APPLICABILITY

The optical recording medium reproducing apparatus according to thisinvention can be used as an optical disc reproducing apparatus.

The optical recording medium reproducing apparatus according to thisinvention can also be used as a reproducing apparatus for opticalrecording media shaped like rectangles instead of discs and in which aplurality of recording tracks are formed so as to be horizontallyaligned.

The reference numerals used on the attached Figures refer to thefollowing elements: 1 . . . optical recording medium reproducingapparatus, 3 . . . spindle motor, 4 . . . disc, 5 . . . optical pickup,6 . . . laser diode, 8 . . . beam splitter, 9 . . . objective lens, 10 .. . lenticular lens, 11 . . . quarterly dividing detector, 12A to 12D .. . amplifying circuit, 13 . . . matrix circuit, 13A . . . focusingerror signal forming circuit, 13B . . . tracking error signal formingcircuit, 13C . . . RF signal forming circuit, 13D . . . tangentialpush-pull signal forming circuit, 13E . . . push-pull signal formingcircuit, 21 . . . summing circuit, 22, 29, 32, 50 . . . phasecompensating circuit, 23, 30, 33, 51 drive circuit, 14 . . . bus, 15 . .. CPU, 16 . . . preset ROM, 17 RAM, 24 . . . focusing actuator, 27 . . .switching circuit, 28 divider, 31 . . . tracking actuator, 34 . . .thread actuator, 35 . . . tracking error signal amplitude detectingcircuit, 40 . . . switching circuit, 41 . . . spindle servo, 38 . . .AGC circuit, 39, 46 . . . RF signal demodulating circuit, 45 tangentialpush-pull signal processing circuit, 55 . . . RF signal amplitudedetecting circuit, 58 . . . asymmetry modulation degree detectingcircuit, 60 . . . absolute time data in the pregroove demodulatingcircuit, 70 . . . operation input key.

What is claimed is:
 1. An optical recording medium reproducing apparatusfor reproducing information recorded on an optical recording medium witha plurality of pits formed along recording tracks based on said recordedinformation, comprising:a laser beam emitting means for emitting a laserbeam; a focus control means for controlling the focusing of said laserbeam on said optical recording medium; a control means for controllingsaid focus control means so as to increase the spot diameter of thelaser beam emitted onto said optical recording medium when the mediumhas a low recording density with pits relatively sparsely arrangedcompared to the case in which the medium has a high recording densitywith pits relatively densely arranged, wherein said control meanssupplies different focus bias values to said focus control meansdepending upon whether said optical recording medium has a high or a lowrecording density, and a storage means for storing high and lowrecording density focus bias values.
 2. An optical recording mediumreproducing apparatus according to claim 1 wherein said focus controlmeans:a focus detecting means for detecting the focusing of said laserbeam on said optical recording medium, wherein said focus detectingmeans controls the focusing of said laser beam emitting means based on afocus bias value set by said control means and an output signal fromsaid focus detecting means.
 3. An optical recording medium reproducingapparatus for reproducing information recorded on an optical recordingmedium with a plurality of pits formed along recording tracks based onsaid recorded information, comprising:a laser beam emitting means foremitting a laser beam; a focus control means for controlling thefocusing of said laser beam on said optical recording medium; a controlmeans for controlling said focus control means so as to increase thespot diameter of the laser beam emitted onto said optical recordingmedium when the medium has a low recording density with pits relativelysparsely arranged compared to the case in which the medium has a highrecording density with pits relatively densely arranged, wherein saidcontrol means supplies different focus bias values to said focus controlmeans depending upon whether said optical recording medium has a high ora low recording density; a light receiving means for receiving a laserbeam reflected from said optical recording medium; and a read signalgenerating means for generating a read signal for said recordedinformation based on an output signal from said light receiving means,wherein: said control means controls said focus bias value so that saidread signal will have a maximum value.
 4. An optical recording mediumreproducing apparatus according to claim 3 whereinsaid control meansfurther provides different focus bias values depending upon theapparatus executes reproduction or a track jump.
 5. An optical recordingmedium reproducing apparatus according to claim 3 whereinsaid controlmeans varies said focus bias value from a predetermined value to set asan adjusted focus bias value, the focus bias value obtained when saidread signal has a maximum value.
 6. An optical recording mediumreproducing apparatus according to claim 3 whereinsaid control meansuses a calibration operation to set said focus bias value.
 7. An opticalrecording medium reproducing apparatus according to claim 3 whereinsaidcontrol means uses a calibration operation to set at least a focus biasvalue for said low recording density recording medium.
 8. An opticalrecording medium reproducing apparatus according to claim 7 furthercomprising:a storage means for storing default high and low recordingdensity focus bias values, wherein: said control means uses as aninitial value one of said default high and low recording density focusbias values to perform a calibration operation in order to adjust saidinitial value.
 9. An optical recording medium reproducing apparatusaccording to claim 8 further comprising:a light receiving means forreceiving a laser beam reflected from said optical recording medium; andan error detecting means for detecting the error condition of an outputsignal from said light receiving means wherein: said control means setsas said initial value one of said default high and low recording densityfocus bias values based on the error condition of the output signal fromsaid light receiving means.
 10. An optical recording medium reproducingapparatus according to claim 9 further comprising:a storage means forstoring the relationship between information data and a preset valuewherein: said control means reproduces information data recorded in thepredetermined region of said optical recording medium using said defaulthigh or low recording density focus bias value based on the outputsignal output from said light receiving means, and wherein when thereproduced information data matches any information data stored in saidstorage means, said control means sets said focus bias value at a presetvalue relating to the matching data.
 11. An optical recording mediumreproducing apparatus for reproducing information recorded on an opticalrecording medium with a plurality of pits formed along recording tracksbased on said recorded information, comprising:a laser beams emittingmeans for emitting a laser beam; a focus control means for controllingthe focusing of said laser beam on said optical recording medium; acontrol means for controlling said focus control means so as to increasethe spot diameter of the laser beam emitted onto said optical recordingmedium when the medium has a low recording density with pits relativelysparsely arranged compared to the case in which the medium has a highrecording density with pits relatively densely arranged, whereinsaidcontrol means supplies different focus bias values to said focus controlmeans depending upon whether said optical recording medium has a high ora low recording density, and a light receiving means for receiving alaser beam reflected from said optical recording medium; and a readsignal generating means for generating a read signal for said recordedinformation based on an output signal from said light receiving means;and, wherein said focus control means comprises a servo error signalgenerating means for generating a servo error signal indicating a servoerror of said laser emitting means relative to said optical recordingmedium, based on an output signal from the light receiving means,wherein: said control means uses said read signal to set said focus biasvalue so that said servo error signal will have a predetermined value.12. An optical recording medium reproducing apparatus according to claim11 whereinsaid servo error signal is a tracking error signal.
 13. Anoptical recording medium reproducing apparatus according to claim 11whereinsaid servo error signal is a differential push-pull signal. 14.An optical recording medium reproducing apparatus for reproducinginformation recorded on an optical recording medium with a plurality ofpits formed along recording tracks based on said recorded information,comprising:a laser beam emitting means for emitting a laser beam; afocus control means for controlling the focusing of said laser beam onsaid optical recording medium; a control means for controlling saidfocus control means so as to increase the spot diameter of the laserbeam emitted onto said optical recording medium when the medium has alow recording density with pits relatively sparsely arranged compared tothe case in which the medium has a high recording density with pitsrelatively densely arranged, wherein said control means suppliesdifferent focus bias values to said focus control means depending uponwhether said optical recording medium has a high or a low recordingdensity; a light receiving means for receiving a laser beam reflectedfrom said optical recording medium; and a read signal generating meansfor generating a read signal relating to said recorded information basedon an output signal from said light receiving means; and, wherein saidfocus control means comprises a servo error signal generating means forgenerating a servo error signal indicating a servo error of said laseremitting means relative to said optical recording medium, based on anoutput signal from the light receiving means, wherein: said controlmeans sets said focus bias value at a value that meets a first conditionin which said read signal is larger than or equal to a first thresholdand in which said servo error signal has a value larger than or equal toa second threshold.
 15. An optical recording medium reproducingapparatus according to claim 14, whereinsaid control means sets as anadjusted focus bias value one of focus bias values meeting said firstcondition which also meets a second condition that said read signal hasa value closest to said maximum value.
 16. An optical recording mediumreproducing apparatus according to claim 14 whereinsaid control meanssets as an adjusted focus bias value one of focus bias values meetingsaid first condition which also meets a second condition that said servoerror signal has a value closest to said maximum value.
 17. An opticalrecording medium reproducing apparatus according to claim 16 whereinsaidservo error signal is a tracking error signal.
 18. An optical recordingmedium reproducing apparatus for reproducing information recorded on anoptical recording medium with a plurality of pits formed along recordingtracks based on said recorded information, comprising:a laser beamemitting means for emitting a laser beam; a focus control means forcontrolling the focusing of said laser beam on said optical recordingmedium; a control means for controlling said focus control means so asto increase the spot diameter of the laser beam emitted onto saidoptical recording medium when the medium has a low recording densitywith pits relatively sparsely arranged compared to the case in which themedium has a high recording density with pits relatively denselyarranged, wherein said control means supplies different focus biasvalues to said focus control means depending upon whether said opticalrecording medium has a high or a low recording density; a lightreceiving means for receiving a laser beam reflected from said opticalrecording medium; a read signal generating means for generating a readsignal for said recorded information based on an output signal from saidlight receiving means; and, wherein said focus control means comprises aservo error signal generating means for generating a servo error signalindicating a servo error of said laser emitting means relative to saidoptical recording medium, based on an output signal from the lightreceiving means, wherein: said control means sets as an adjusted focusbias value a value that meets the first condition and which isdetermined on the basis of a first range of said focus bias values thatserve to provide said read signal that exceeds said first threshold anda second range of said focus bias values that serve to provide saidservo error signal that exceeds said second threshold.
 19. An opticalrecording medium reproducing apparatus according to claim 18 whereinsaidcontrol means sets as the adjusted focus bias value a central value ofthe area in which said first and second ranges of focus bias values thatmeet said first condition and overlap each other.